I mean, are you asking how to pronounce her name as well as what it means? If so, Reissa is kinda pronounced "Lreh-ee-sah", the Lr combination meaning a "flattened" r, which I describe as somewhere between "l" and "r", and a "quickened" vowel sound (perhaps somewhere around the length of a transient thought, but that's just how I kinda time Japanese short vowels.)
As for what it means, have you asked her to show you the kanji for her name? The kanji, along with the pronunciation, determines what a word (including a name) means.
I hope I've helped you some. :)
Phyllis (aka Sidhe Uaine or
Gaia Euphoria)